I just spent a little while this afternoon prising the cover off my light sensor. I managed it without breaking anything. I have fashioned a temporary dust-cover using a bit of polythene and "super-clear" Sellotape, which doesn't degrade in light the way the normal stuff does. We'll see how long it lasts! Pro tip. It looks really, really naff.
Going forward, I hope
@TrullT will be able to produce 3D printed covers from Pliskin's file. Failing that, I'll drill a hole in the original cover as others have indicated. Supposedly, this does the trick.